The present invention relates to an electricity demand limiting system for resistive loads that is controlled using at least one of a schedule, a real time condition control signal, a user defined willingness to pay decision table, a device or premise demand management system, a thermostatic control system or other monitoring and control systems or method.
In some states and countries where the major form of energy available to a customer premises is electricity, demand metering systems are deployed to encourage customers to keep their total demand as flat as possible. Demand, from an electricity supplier's perspective, is the instantaneous need for energy to satisfy loads within a customer premise. Resistive loads create a fairly flat demand on the energy delivery system when operating at full capacity. Resistive loads typically are large heating elements that consume a large amount of energy when energized and typically operate under the control of a thermostatic controller. Because the load is resistive and large, it represents a significant portion of the total demand placed on an energy delivery system by the customer premise.
Reactive loads, on the other hand, are typically rotating devices like motors. Reactive loads produce an initial high demand for energy to get the stationary armature moving. Once in motion, the total demand is reduced as the load reaches operating speed. These two very different types of loads make up the majority of the electric load found in a premise. Because the utility serving the premise has to provide enough energy to meet the demand placed on it at any time, the concept of demand metering has been adopted in some areas.
Demand metering continuously monitors the total demand at a premise and records the peak demand for each billing period. In some utility power supply systems outside the US, the meters on each home are programmed with a disconnect relay that will cut all power to the home if the demand exceeds a predetermined level. These relays can only be reset by the utility and are designed to force premise owners to stay under designated demand levels.
In the United States, the rate used for energy billing to commercial/industrial and some residential accounts is based upon the peak demand for the billing period and the total energy consumption. The definition of a “peak period” can vary from an instantaneous peak at one extreme, to the highest 15 minute energy demand period recorded for the month. The peak demand is then used to set the rate at which all consumption for the month will be billed. If the demand is low, the rate could, for example, be 6 cents per KWH of energy or less; if the demand is high, it could be as much as 25 cents per KWH. By using demand metering, the utility can recover the costs associated with meeting the maximum demands of the consumer, while not penalizing those customers who keep their demand on the system at a more consistent level.